1. Field of the Invention
The present invention relates to a wireless communication method. The present invention particularly relates to a method for wireless communication between a semiconductor device which transmits and receives a signal, that is, RFID (radio frequency identification) tag and an external communication device.
Note that a semiconductor device here refers to a general device which can function using semiconductor characteristics.
2. Description of the Related Art
Owing to development of computer technologies and improvement of image recognition technologies, data identification methods utilizing media such as barcodes have spread widely and have been used for identification of product data and the like. It is expected that the amount of data to be identified will further increase in the future. On the other hand, data identification utilizing barcodes is disadvantageous in that a barcode reader is required to be in contact with the barcodes, and that the amount of data capable of being stored in the barcodes is not so large. Therefore, contactless data identification and increase in the storage capacity of a medium have been required.
In view of the foregoing requirements, an RFID tag (hereinafter referred to as a semiconductor device, and also referred to as an ID chip, an IC tag, an ID tag, an RF tag, a wireless tag, an electronic tag, or a transponder) utilizing semiconductor characteristics and a wireless communication device (hereinafter referred to as a communication device, and also referred to as a reader/writer, a controller, or an interrogator) having a function of communicating with a semiconductor device have been developed. A semiconductor device stores necessary data in a storage element of the semiconductor device and reads the data by the communication device with the use of a contactless means, generally a wireless signal. It is expected that practical application of such a wireless communication system for reading data stored in a semiconductor device will allow commercial distribution and the like to be simplified and reduced in cost while ensuring high security.
In recent years, a system with which data can be transmitted and received without contact in a variety of fields where automatic identification is necessary, such as payment for goods, has spread widely. A product on which such a semiconductor device is mounted is designed so as to read and write data from/to an external device without contact through an antenna having a shape suited to a frequency band used at the time of transmission or reception of data.
A semiconductor device which performs wireless communication can read a signal from a plurality of semiconductor devices by providing an anti-collision function (also referred to as anti-collision simply) in a communication device, unlike reading of two-dimensional data such as barcodes. Further, a semiconductor device which performs wireless communication can transmit and receive a wireless signal even if there is an obstacle between a communication device and the semiconductor device, unlike reading of two-dimensional data such as barcodes. In the case where there is an obstacle between a communication device and the semiconductor device and accordingly a wireless signal cannot be transmitted and received, a repeater for transmitting and receiving the wireless signal is provided to secure identification information of a desired semiconductor device (see Patent Document 1: Japanese Published Patent Application No. 2001-24547).